Funny you should ask this today, as I've been going through all my cookbooks for the purpose of culling/downsizing - preparing for a big kitchen remodel. I went from 6 shelves of cookbooks to 3. I COULD NOT part with these two Thai cookbooks: RealThai (Nancie McDermott) and The Food of Thailand (published by Periplus World Cookbooks). The former covers Thai cooking from the different regions of Thailand and seems very authentic - no ingredient too obscure; the latter seems to be geared more toward the western cook. I usually use them together (recipe mashups, a bad habit). Everything has always turned out great. Also, many years ago a Thai friend recommended a book called Thai Cooking for American Kitchens - but I've never been able to find that. And now I am craving Tom Kha Gai and sticky rice with mango!

Asian grocery store demystified by Linda Bladholm. great for better shopping, learning your way around foodstuffs which may have little or no English on package.
world of the east vegetarian cooking by Madhur Jaffrey. gives great recipes for many countries, from japan in east to Middle East in west. even if you're not vegetarian, it can still point you to traditional dishes, to which you can restore the meat.
Jean-Georges: cooking at home with a four-star chef, Jean-Georges Vongerichten. French chef who cooked for years in Asia. includes his chicken soup that was served from beginning to end of Vong, NYC restaurant. he doesn't call it that, but it's a great version of Tom Kha Gai.
his recipe is also here:
http://leitesculinaria...